Radial folded fin heat sink

ABSTRACT

A heat sink for cooling a microelectronic device, and methods of manufacturing and operating the heat sink. The heat sink includes a plurality of fins, folded from a strip of thermally conductive material, arranged in a radial pattern. A fan may be disposed at a center of the radial pattern to direct airflow radially outward over the folded fins.

BACKGROUND OF THE INVENTION

[0001] 1. Technical Field of the Invention

[0002] The present invention relates generally to heat sinks for coolingsemiconductor devices or the like, and more specifically to an improvedfin structure for such.

[0003] 2. Background Art

[0004] Heat sinks are known in a variety of configurations, both withand without fans. Heat sink designers struggle to balance thermalefficiency against manufacturing cost. Finned heat sinks use a number offins to increase surface area and thereby improve thermal performance.Fins are generally formed by casting or by machining, both of whichcontribute significantly to manufacturing cost.

[0005] U.S. Pat. Nos. 5,785,116 and 5,975,194 describe heat sinks withfins radially arranged about a central fan, to improve thermalperformance and noise generation.

[0006] What is desired is a radial fin heat sink which has reducedmanufacturing cost but which offers adequate thermal performance.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The invention will be understood more fully from the detaileddescription given below and from the accompanying drawings ofembodiments of the invention which, however, should not be taken tolimit the invention to the specific embodiments described, but are forexplanation and understanding only.

[0008]FIG. 1 shows one embodiment of a folded fin heat sink.

[0009]FIG. 2 shows another embodiment of a folded fin heat sink,including a collar.

[0010]FIG. 3 shows another embodiment of a folded fin heat sink,including a fan mounted within the folded fins.

[0011]FIG. 4 shows airflow through the folded fin heat sink shown inFIG. 3, and shows additional details of a base of the folded fin heatsink.

[0012]FIG. 5 shows another embodiment of a folded fin heat sink,including a fan mounted atop the folded fins.

[0013]FIG. 6 shows airflow through the folded fin heat sink shown inFIG. 5, and shows additional details of a base of the folded fin heatsink.

[0014]FIG. 7 shows another embodiment of a base for a folded fin heatsink.

[0015]FIG. 8 shows another embodiment of a folded fin heat sink, havingtwo folded fin cores.

[0016]FIG. 9 shows another embodiment of a folded fin heat sink, havingimproved airflow at its center.

[0017]FIG. 10 shows one embodiment of a sheet for forming a folded finheat sink such as that shown in FIG. 9.

[0018]FIG. 11 shows another embodiment of a sheet for forming a foldedfin heat sink such as that shown in FIG. 9.

[0019]FIG. 12 shows one embodiment of a folded fin heat sink such as maybe formed from the sheet of FIG. 10 or 11.

[0020]FIG. 13 shows another embodiment of a folded fin heat sink such asmay be formed from the sheet of FIG. 10 or 11.

[0021]FIG. 14 shows another embodiment of the folded fin heat sink inwhich the tops of the folded fins are open.

DETAILED DESCRIPTION

[0022]FIG. 1 illustrates one embodiment of the folded fin heat sink 10of the present invention. The folded fin heat sink includes one or morefolded fin members 12 arranged in a radial orientation generally about acenter axis of the heat sink. In some embodiments, the folded fin membermay be constructed as one unitary member, while in others it may beconstructed as two or more members which may optionally be joined toeach other. In other words, the entire group of folded fins may beconstructed from one piece, or from two or more pieces.

[0023] The folded fin member includes a plurality of fins 18 having aheight H and a width W. In one embodiment, the fins all havesubstantially the same height and width, while in other embodiments, thevarious fins may have differing heights and/or widths.

[0024] In various embodiments, the folded fin member may be folded so asto have laterally extending top segments 14 of dimension Y, or alaterally extending bottom segments 16 of dimension Z, or both.Inclusion of the laterally extending segments serves to provide spacingbetween adjacent fins, to improve airflow, albeit at the expense ofreducing the total number of fins.

[0025] Those of skill in the art will understand how to selectappropriate height H, width W, top dimension Y, and bottom dimension Z,as well as the overall radius of the heat sink, the material from whichto make the folded fins, the thickness of that material, and so forth,to balance the thermal performance, size, cost and so forth of the heatsink for usage in a given application.

[0026]FIG. 2 illustrates the optional addition of a cap 20 and a base22. The cap may serve to stabilize the fins and keep them from beingeasily bent, and may offer somewhat increased surface area for thermaltransfer. It may also serve to direct airflow. The base may serve as aprimary thermal interface between the folded fins and the device (notshown) to be cooled.

[0027] The folded fins, the cap, and the base may, in some embodiments,be constructed of metals such as copper or aluminum. In one embodiment,the base is a copper alloy and the fins are an aluminum alloy. In someembodiments, the folded fins may be brazed to the base to improvethermal transfer from the base to the folded fins. In other embodiments,less expensive methods such as epoxy may be used to affix the foldedfins to the base. In the least expensive embodiments, the folded finscould simply be touching the base, and could be held in place by, forexample, being held captive between the cap and base. The skilledengineer will understand how to make appropriate cost/performancetradeoffs for the particular application at hand.

[0028]FIG. 3 illustrates the addition of a fan 26 to the heat sink. Insome such embodiments, a cap (not shown) may be added, and its inner andouter diameters selected, to appropriately direct airflow, such as tominimize recirculation.

[0029]FIG. 4 illustrates the fan-equipped radial folded fin heat sink incross-section. The fan 26 is disposed within the folded fins 18, and ismounted to the base 22. The base is thermally coupled to the device 30which is to be cooled, such as a semiconductor or other microelectronicdevice. The base may in some cases ride on a layer of thermal grease(not shown) which serves to improve thermal transfer by filing in tinyvoids which are due to irregularities in the mating surfaces of the baseand/or the microelectronic device.

[0030] In some embodiments, the fan may draw air in, in a generallyaxial direction, and expel it outward through the folded fins, assuggested by the arrows. In other embodiments, this flow may bereversed, as the application indicates.

[0031] In some embodiments, it may be found desirable to shape the topand/or bottom surfaces of the base. It has been found that overallthermal conductivity depends in some measure upon the thickness of thecentral region of the base, generally about the microelectronic device,while maintaining that thickness toward the perimeter does notproportionately contribute to overall thermal conductivity. Butthickness does contribute directly to weight, and thickness at theperimeter more than linearly contributes to stress on themicroelectronic device under shock or vibration. Thus, by having abeveled or otherwise reduced outer portion 32 of the upper surface, anda beveled or otherwise reduced outer portion 28 of the lower surface,the weight of the base is reduced without significantly reducing thermalperformance.

[0032]FIG. 5 illustrates another embodiment of the fan-equipped radialfolded fin heat sink, in which the fan 26 is mounted externally to thefolded fins rather than within their dimensions. In some embodiments, ahybrid of the embodiments of FIGS. 4 and 5 could be used, in which, forexample, the motor of the fan is located external to the folded fins,while the propeller blades or other air-moving apparatus is locatedwithin the dimensions of the folded fins. In some embodiments, the fanblades may be partly within the folded fin structure and partly outsideit. In some embodiments, circulation devices other than fans may beemployed, such as blowers or jets.

[0033]FIG. 6 illustrates one embodiment of a base 22 which may beutilized in conjunction with the externally located fan. In some suchapplications, airflow and thermal performance may be increased byfabricating the base so as to give it a raised, central portion 34. Insome embodiments, this raised, central portion may be substantiallyconical. The reader will appreciate that the folded fins 18 shown inFIG. 6 are not coupled to the conical section, but are merely seen asbeing behind it. The skilled person will be able to select anappropriate shape of the central portion, based upon the application'sthermal and cost and weight requirements.

[0034]FIG. 7 illustrates another embodiment of the conical centralportion 34, shown in top view. In this embodiment, the central portion34 of the base 22 has been machined or otherwise fabricated to includeone or more channels 36 between two or more central portion members 38.In one such embodiment, the channels are cut in two directions, leavingrectilinear posts as the central portion members. This increases thesurface area of the central portion 34. In other embodiments, theseposts could be formed with, for example, round cross section.

[0035]FIG. 8 illustrates, in top view, another embodiment of the radialfolded fin heat sink, in which two or more rings 40, 42 of folded finsare utilized. In any radial configuration, the intra-fin spacing issmaller at the fins' inner edges than at their outer edges. Oneadvantage of the multiple-ring embodiment is that it allows for are-spacing to increase total folded fin surface area. In other words,the outer ring can include more total fins than the inner ring, withoutviolating a minimum intra-fin spacing requirement. The inner ring 40 hasfins 18 at a given spacing, and the outer ring 42 has fins 44 at aspacing which is tighter than the spacing at the outer edge of the innerring's fins 18.

[0036] Thermal conductivity is increased in areas of flow and thermalboundary layer development. Once a boundary layer has formed or fullydeveloped and laminar flow is established, thermal conductivity isreduced. By breaking the folded fins into multiple rings, it may in someembodiments be possible to increase the total surface area of boundarylayer development. In such cases, it will be desirable to selectrelative spacings such that the number of lined-up folded fins isminimized, as between folded fins of adjacent rings.

[0037]FIG. 9 illustrates, in top view, another embodiment of a radialfolded fin heat sink, which addresses the issue of minimum innerspacing. For a given number of radial folded fins of a given thickness,as those fins are extended inward, the spacing between them decreases.At some point, there may not be enough space to provide adequate airflowfor a given application. However, backing the inner edge away from thecenter has the effect of reducing the folded fins' surface area. Onesolution, shown in FIG. 9, is to utilize folded fins 18 a, 18 b whichextend to different distances Ra, Rb from the center. One embodimentemploys folded fins of differing width (W, as shown in FIG. 1).Sufficient space is maintained between adjacent fins 18 a that extend tothe inner distance Ra, yet the other fins 18 b contribute significantlyto the total surface area. While, for simplicity, only two such sizesare shown, any number of sizes may be utilized, in a variety ofconfigurations.

[0038] Furthermore, while FIG. 9 illustrates an embodiment in whichevery second fin ends a greater distance from the axis than does itsneighbors, other embodiments are within the scope of this invention. Forexample, there may be multiple different lengths. Or, each folded fin ina pair may share a common width, with alternating pairs being ofdifferent width.

[0039]FIG. 10 illustrates a strip of material 50 which may be utilizedin manufacturing the folded fins of FIG. 9. The strip includes a toothedor serrated edge 52 which forms the inner edges of the folded fins. Inone embodiment, the strip is folded at the dashed lines A-D, which inone embodiment surround respective edges of the serration. The materialbetween two adjacent folds A, B forms the laterally extending topsegment (14 in FIG. 1), while the material between two other adjacentfolds C, D forms the laterally extending bottom segment (16 in FIG. 1),or vice versa. The material between adjacent folds B, C of respectiveadjacent pairs of folds forms the folded fin itself (of dimension H inFIG. 1) and has an inner edge 52. The material between the fold D and afold A of a next set of folds (not shown) would form the next foldedfin, and has an inner edge 54. The first inner edge 52 forms the finwhich extends more toward the center of the heat sink, while the secondinner edge 54 forms the fin which stops short of its neighboring fins.While only two depths of fins are shown in FIG. 10, the reader willappreciate that other depths can readily be produced using this samemethod.

[0040] The reader will notice that the fold pairs A, B and C, D eachencompasses a portion of the edge of the material where the depthtransition is made. In another embodiment, illustrated at fold pairs E,F and G, H, the folds may be made outside the transition points. In suchembodiments, the teeth or serrations will not have a 50:50 “duty cycle”.

[0041]FIG. 11 illustrates yet another embodiment of the strip ofmaterial, in which the serrations are not square. In one such embodimentthey may have a sinusoidal shape. In other embodiments, other shapes maybe used. The fold pairs J, K and L, M may be positioned as with foldpairs A,B and C,D, or as with fold pairs A, B and C, D in FIG. 10.

[0042] In some applications, it may not be necessary that the entirevertical dimension (H of FIG. 1) of adjacent fins be completely onelength (to Ra or to Rb in FIG. 8). In such applications, the roundedshape of FIG. 11 may be suitable.

[0043] Other edge shapes are within the scope of this invention. Forexample, the edge may be generally saw-toothed but have roundedtransitions between the teeth, rather than the 90° angles shown in FIG.10.

[0044]FIG. 12 illustrates a folded fan heat sink made from the strip ofFIG. 10 and folded at lines A-D in FIG. 10. The edge 56 of the tooth inFIG. 10 is included within the laterally extending top segment of thefolded fins in FIG. 12, while the longitudinal edges 54 and 56 in FIG.10 become the centermost edges of respective folded fins. (For ease inillustration, the edge 52 is shown for a different tooth in FIG. 12.)

[0045]FIG. 13 illustrates an alternative embodiment, in which the stripis folded differently, resulting in a first folded fin pair 60 extendingfarther toward the axis than the fins of a second folded fin pair 62.Each of the fins of any given pair are of a substantially same width.

[0046]FIG. 14 illustrates another embodiment of the folded fin heatsink, in which the respective folded fin pairs are separate from eachother. One method of fabricating this embodiment is to separately bendthe pairs and separately affix them to the base. Another method is tofabricate them as a ring, affix them to the base, and remove thelaterally extending top segments to separate the pairs. This embodimentmay provide improved downward airflow, as both sides of all fins areexposed from the top, rather than having the laterally extending topsegments blocking downward airflow between every other pair of adjacentfins.

[0047]FIG. 15 illustrates yet another embodiment, in which the foldedfins 18 are shaped to allow them to contact the raised central portion34 of the base 22. This permits greater fin surface area. In some suchembodiments, the fins may end short of the axis, leaving room for asmall fan. In other embodiments, the fins may extend substantially tothe axis.

[0048] One method of fabricating such an embodiment as shown in FIG. 15is to fabricate the folded fins from an appropriately-shaped strip ofmaterial having a complex edge. Another is to fabricate the folded finsfrom a strip which is generally rectangular or which is substantially asshown in FIG. 10 or 11, and to slot the raised central portion of thebase to permit insertion of the fins into it, as suggested by the dashedline 72.

[0049] Finally, the reader will appreciate that a variety ofmanufacturing methods may be employed. In one method, the strip ofmaterial is folded while in a substantially linear configuration, andthe resulting linear folded fin is bent around a mandrel to give it itsradial configuration. In another method, a plurality of individual finsmay be separately affixed to the base without any folding. In another, aplurality of strips are folded and affixed to the base in an N-agonalarrangement such that not all of the fins are strictly radial but theoverall arrangement is substantially radial. In another, individual finpairs may be folded from strips and separately affixed to the base.

[0050] Reference in the specification to “an embodiment,” “oneembodiment,” “some embodiments,” or “other embodiments” means that aparticular feature, structure, or characteristic described in connectionwith the embodiments is included in at least some embodiments, but notnecessarily all embodiments, of the invention. The various appearances“an embodiment,” “one embodiment,” or “some embodiments” are notnecessarily all referring to the same embodiments.

[0051] If the specification states a component, feature, structure, orcharacteristic “may”, “might”, or “could” be included, that particularcomponent, feature, structure, or characteristic is not required to beincluded. If the specification or claim refers to “a” or “an” element,that does not mean there is only one of the element. If thespecification or claims refer to “an additional” element, that does notpreclude there being more than one of the additional element.

[0052] Those skilled in the art having the benefit of this disclosurewill appreciate that many other variations from the foregoingdescription and drawings may be made within the scope of the presentinvention. Indeed, the invention is not limited to the details describedabove. Rather, it is the following claims including any amendmentsthereto that define the scope of the invention.

What is claimed is:
 1. An apparatus comprising: a thermally conductivebase having a center; and a plurality of folded fins coupled to the baseso as to be oriented substantially radial to the center of the base. 2.The apparatus of claim 1 further comprising: the plurality of foldedfins being brazed to the base.
 3. The apparatus of claim 1 wherein: theplurality of folded fins comprise a monolithic folded strip.
 4. Theapparatus of claim 3 further comprising: a plurality of monolithicfolded strips coupled together, each comprising a plurality of foldedfins.
 5. The apparatus of claim 1 wherein: the plurality of folded finscomprise a metallic composition.
 6. The apparatus of claim 5 wherein:the metallic composition of the folded fins comprises aluminum.
 7. Theapparatus of claim 5 wherein: the base comprises a metallic composition.8. The apparatus of claim 7 wherein: the metallic composition of thebase comprises copper.
 9. The apparatus of claim 8 wherein: the metalliccomposition of the folded fins comprises aluminum.
 10. The apparatus ofclaim 1 wherein: the base comprises a center portion and an outerportion which is thinner than the center portion.
 11. The apparatus ofclaim 10 wherein: the center portion comprises a raised portion having asubstantially conical shape which extends within a dimension of thefolded fin member.
 12. The apparatus of claim 11 wherein: the raisedportion of the base comprises a plurality of posts separated by airflowchannels.
 13. An apparatus comprising: a thermally conductive base; afolded fin member coupled to the base and including a plurality offolded fins arranged substantially radially to the base; and a fancoupled to at least one of the base and the folded fin member.
 14. Theapparatus of claim 13 wherein: the fan is disposed substantially withina dimension of the folded fin member.
 15. The apparatus of claim 13wherein: the fan is disposed substantially without a dimension of thefolded fin member.
 16. The apparatus of claim 13 further comprising: acap coupled to at least one of the base and the folded fin member,wherein the folded fin member is disposed between the base and the cap.17. The apparatus of claim 16 wherein: the base comprises a raisedcentral portion.
 18. The apparatus of claim 17 wherein: the raisedcentral portion of the base has a substantially conical shape.
 19. Theapparatus of claim 17 wherein: the raised central portion comprises aplurality of posts separated by a plurality of airflow channels.
 20. Anapparatus comprising: a plurality of concentrically disposed rings, eachring including, a plurality of folded fins each oriented substantiallyradially within the apparatus.
 21. The apparatus of claim 20 furthercomprising: a base to which the folded fins are coupled.
 22. Theapparatus of claim 20 wherein: the plurality of folded fins of a firstring of the plurality of concentrically disposed rings has a firstintra-fin spacing at an outer circumference of the first ring; and theplurality of folded fins of a second ring of the plurality ofconcentrically disposed rings has a second intra-fin spacing at an innercircumference of the second ring, wherein the second intra-fin spacingis closer than the first intra-fin spacing.
 23. The apparatus of claim20 wherein: the plurality of folded fins of an outer ring of theplurality of concentrically disposed rings comprises a greater number offolded fins than the plurality of folded fins of an inner ring of theplurality of concentrically disposed rings.
 24. The apparatus of claim20 wherein: the folded fins of first and second adjacent rings of theplurality of concentrically disposed rings are disposed such that thefolded fins of the first ring are substantially non-aligned with thefolded fins of the second ring.
 25. An apparatus comprising: a firstplurality of fins each disposed substantially radially within theapparatus and extending to a first distance from a radial center of thefirst plurality of fins; and a second plurality of fins each disposedsubstantially radially within the apparatus and extending to a seconddistance from the radial center; wherein the fins of the secondplurality of fins are interspersed among the first plurality of fins;and the second distance is greater than the first distance.
 26. Theapparatus of claim 25 wherein: the fins of the first plurality and thefins of the second plurality are disposed alternately.
 27. The apparatusof claim 25 wherein: the fins of the first plurality and the fins of thesecond plurality comprise a monolithic structure.
 28. The apparatus ofclaim 27 wherein: the fins of the first plurality and the fins of thesecond plurality comprise fins folded from a strip having a serratededge.
 29. The apparatus of claim 28 wherein: the serrated edge has asubstantially square tooth configuration.
 30. The apparatus of claim 29wherein: the fins of the first plurality are formed from protrudingportions of the square tooth configuration; and the fins of the secondplurality are formed from non-protruding portions of the square toothconfiguration.
 31. The apparatus of claim 30 wherein: the fins areformed by fold pairs, each fold pair surrounding a transition from oneof the protruding portion and the non-protruding portion to the other.32. The apparatus of claim 28 wherein: the serrated edge has asubstantially sinusoidal configuration.
 33. A method of manufacturing aheat sink, the method comprising: folding a strip of thermallyconductive material into a first plurality of folded fins; thermallycoupling the plurality of folded fins to a thermally conductive base ina radial arrangement.
 34. The method of claim 33 further comprising:prior to coupling the first plurality of folded fins to the thermallyconductive base, bending the folded strip around a mandrel to give thefins the radial arrangement.
 35. The method of claim 33 wherein: thethermally coupling the first plurality of folded fins to the thermallyconductive base comprises brazing bottom segments of the fins to thebase.
 36. The method of claim 33 further comprising: coupling a cap tothe first plurality of folded fins in a configuration such that thefolded fins are disposed between the base and the cap.
 37. The method ofclaim 33 further comprising: coupling a fan to the base.
 38. The methodof claim 37 further comprising: disposing the fan within the fins. 39.The method of claim 33 further comprising: fabricating the base to givethe base a center portion having a greater thickness than an outerportion of the base.
 40. The method of claim 39 further comprising:fabricating the center portion of the base to have a substantiallyconical shape to extend within the fins.
 41. The method of claim 40further comprising: fabricating the center portion to include aplurality of posts and a plurality of airflow channels between theposts.
 42. The method of claim 33 further comprising: folding a secondstrip into a second plurality of folded fins; and thermally coupling thesecond plurality of folded fins to the thermally conductive base,disposed concentrically about the first plurality of folded fins. 43.The method of claim 42 further comprising: spacing the folded fins ofthe second plurality to have a spacing at an inner circumference of thesecond plurality which is tighter than an outer circumference spacing ofthe folded fins of the first plurality.
 44. The method of claim 43further comprising: prior to the thermally coupling the second pluralityof folded fins to the thermally conductive base, aligning the secondplurality of folded fins with the first plurality of folded fins tosubstantially minimize instances where given ones of the first pluralityare in radial alignment with given ones of the second plurality.
 45. Themethod of claim 33 further comprising: serrating an edge of the stripwhich forms an inner circumference of the first plurality of foldedfins.
 46. The method of claim 45 wherein: the serrating comprisesmanufacturing the strip to give the edge a substantially square toothpattern.
 47. The method of claim 46 wherein: the serrating comprisesmanufacturing the strip to give the edge a substantially sinusoidaltooth pattern.
 48. The method of claim 45 wherein: the folding comprisescreating a plurality of fold pairs, wherein alternating ones of the foldpairs form laterally extending top portions of the folded fins andlaterally extending bottom portions of the folded fins, respectively.49. The method of claim 48 wherein: the creating the plurality of foldpairs comprises encompassing serrations of the edge within fold pairs.50. The method of claim 48 wherein: the thermally coupling the pluralityof folded fins to the thermally conductive base comprises coupling thelaterally extending bottom portions of the folded fins to the base. 51.The method of claim 50 wherein: the coupling the laterally extendingbottom portions of the folded fins to the base comprises brazing. 52.The method of claim 50 wherein: the coupling the laterally extendingbottom portions of the folded fins to the base comprises affixing withepoxy.
 53. A method of cooling a microelectronic device, the methodcomprising: conducting heat from the microelectronic device through abase thermally coupled to the microelectronic device; and conductingheat from the base through a first plurality of radial folded finsthermally coupled to the base.
 54. The method of claim 53 furthercomprising: blowing air over the first plurality of radial folded finsby a fan coupled to at least one of the base and the plurality of radialfolded fins.
 55. The method of claim 53 further comprising: blowing airover the first plurality of radial folded fins; and directing the airradially outward across the first plurality of radial folded fins by asubstantially conical raised center portion of the base.
 56. The methodof claim 55 further comprising: conducting heat from the base to the airby a plurality of posts of the substantially conical raised centerportion of the base.
 57. The method of claim 53 further comprising:conducting heat from the base through a second plurality of radialfolded fins coupled to the base and arranged concentrically with thefirst plurality of radial folded fins.
 58. The method of claim 57wherein the first and second pluralities of radial folded fins aredisposed in a first ring and a second ring, respectively, and the secondring is disposed concentrically outside the first ring, the methodfurther comprising: reinitiating boundary layer development at thesecond ring.
 59. The method of claim 57 wherein the first and secondpluralities of radial folded fins are alternately interspersed, and themethod further comprises: as it moves radially outward, the airencountering the first plurality of radial folded fins before itencounters the second plurality of radial folded fins.